Electron beam devices, in particular a scanning electron microscope (SEM) or a transmission electron microscope (TEM), are used for examining samples in order to obtain insights with regard to the properties and behaviour of samples under specific conditions.
In the case of an SEM, an electron beam (hereinafter also called primary electron beam) is generated using a beam generator. The electrons of the primary electron beam are accelerated to a predeterminable energy and focused by a beam guiding system, in particular an objective lens, onto a sample to be analyzed (that is to say an object to be analyzed). A high-voltage source having a predeterminable acceleration voltage is used for acceleration purposes. Using a deflection unit, the primary electron beam is guided in a raster-type fashion over a surface of the sample to be analyzed. In this case, the electrons of the primary electron beam interact with the material of the sample to be analyzed. In particular, interaction particles and/or interaction radiation arise(s) as a consequence of the interaction. By way of example, electrons are emitted by the sample to be analyzed (so-called secondary electrons) and electrons of the primary electron beam are backscattered at the sample to be analyzed (so-called backscattered electrons). The secondary electrons and backscattered electrons are detected and used for image generation. An imaging of the sample to be analyzed is thus obtained.
An imaging of a sample to be analyzed is one possible form of analysis of the sample to be analyzed. However, further forms of analysis are known. By way of example, the interaction radiation (for example X-ray radiation or cathodoluminescent light) is detected and evaluated in order to obtain conclusions about the composition of the sample to be analyzed.
Furthermore, it is known from the prior art to use combination devices for processing and/or for analyzing a sample, wherein both electrons and ions can be guided onto a sample to be processed and/or to be analyzed. By way of example, it is known for an SEM to be additionally equipped with an ion beam column. Using an ion beam generator arranged in the ion beam column, ions are generated which are used for processing a sample (for example for removing a layer of the sample or for applying material to the sample) or else for imaging. In this case, the SEM serves, in particular, for observing the processing, but also for further analysis of the processed or non-processed sample. In particular, a particle beam device is known having a first particle beam column having a first beam axis, wherein the first particle beam column is adapted for generating a first particle beam. In addition, the known particle beam device has a second particle beam column, which is provided with a second beam axis and which is adapted for generating a second particle beam. The first particle beam column and the second particle beam column are arranged with respect to one another in such a way that the first beam axis and the second beam axis form a first angle of approximately 50°. Furthermore, the known particle beam device has a sample carrier, which is rotatable about a rotation axis. The rotation axis runs through the center of the sample carrier. Furthermore, the rotation axis forms a second angle with the first beam axis and a third angle with the second beam axis. At the sample carrier, a sample can be arranged on a sample holder, wherein the sample has a sample surface to be processed and/or to be analyzed. The sample holder extends along the rotation axis. The sample surface has a surface normal that forms a fourth angle with the rotation axis.
An imaging system which may be built as mentioned above and comprising an electron beam column may comprise a single correction unit or several correction units. The imaging system may additionally comprise an ion beam column. Thus, this imaging system may comprise the electron beam column, the ion beam column and a single correction unit or several correction units. The correction unit is used or the correction units are used for correcting imaging aberrations, in particular chromatic and spherical aberrations. By correcting these aberrations, the imaging resolution of the imaging system may be improved.
A particle beam device having a mirror corrector is disclosed in U.S. Pat. No. 6,855,939 B2, which is incorporated herein by reference. The particle beam device disclosed in this reference comprises a mirror corrector which is arranged between an electron source and an objective lens. The mirror corrector comprises an electrostatic mirror and a magnetic beam deflector. The magnetic beam deflector is arranged between the electron source and the electrostatic mirror on one hand as well as between the electrostatic mirror and the objective lens on the other hand. Additional electrostatic and/or magnetic lenses, deflecting units for deflecting the particle beam, electrostatic or magnetic beam alignment units and/or multipole units—such as quadrupole units or multipole units of a higher order—are provided in the beam path of the known particle beam device between the electron source and the object to be examined. The aforementioned units may be used for achieving high resolution while imaging the sample.
A deflecting unit is used for guiding a particle beam in a particle beam device, for example a particle beam device as mentioned above. The deflecting unit may be used for deflecting and/or aligning particles of the particle beam—for example electrons or ions—onto the beam path of the particle beam device. An electrostatic deflecting unit may comprise a first deflecting electrode and a second deflecting electrode. A supply unit provides a first potential to the first deflecting electrode and a second potential to the second deflecting electrode. If the first potential and the second potential are identical, the particle beam passes the first deflecting electrode and the second deflecting electrode on a straight line along an optical axis of the particle beam device. If the first potential and the second potential are chosen in such a way that they are different, an electrostatic field is generated between the first deflecting electrode and the second deflecting electrode. The electrostatic field results in a deflection of the particle beam towards a desired direction, in particular towards the optical axis or away from the optical axis.
Correction units in the form of quadrupole units or correction units comprising a higher number of poles—such as octupole units or twelve-pole units (so called dodecapole units) may be used for correction of image aberrations, for example astigmatism of the particle beam. The correction units may be implemented by any kind of multipole system and, therefore, are not restricted to quadrupole units, octupole units or twelve-pole units. All electrodes of the unit may be arranged in a circle.
It is desirable that the potentials applied to the first deflecting electrode and the second deflecting electrode be rather stable. In other words, it is desirable that the signal-to-noise-ratio VE/VN with respect to the first and second deflecting electrodes be about 105 to 108, wherein VE is the potential applied to the electrodes and VN is the noise potential. VN is determined using the Root-Mean-Square (RMS) method. To achieve such a desirable signal-to-noise-ratio, it is known from the prior art to apply a potential V in the range of 100 V to 10 kV, for example, and to use first and second deflecting electrodes having rather small dimensions, in particular being smaller than 5 mm in length. However, when using small first and second deflecting electrodes, the structural conditions with respect to adjustment of the first and second deflecting electrodes might lead to misguiding of the particle beam. To overcome this problem, it is known to use first and second deflection electrodes each having a length of more than 5 mm. In this case, however, one has to choose low potentials, for example in the range of 10 V to 50 V. However, disturbances due to existing alternating fields in the range of a few μV to a few hundred μV may lead to misguiding of the particle beam. If the connecting line between the supply unit and the first and second deflecting electrodes is long, for example 1 m to 10 m, high frequency disturbances might affect the signal-to-noise-ratio by deteriorating it. The range of the frequencies of those disturbances depends on the range of the length of the connecting lines. The frequencies of those disturbances may be in the range of 10 to 100 MHz if the connecting lines have a length in the range of 1 m to 10 m.
With regard to the prior art, reference is made, for example, to DE 10 2010 007 777 A1, U.S. Pat. No. 6,278,124 B1 and U.S. Pat. No. 8,421,028 B2, which are incorporated herein by reference.
In view of the aforesaid, it would be desirable to provide a particle beam device with an electrode unit, for example a deflection unit, a quadrupole unit or a correction unit, having low high frequency disturbances and a high signal-to noise-ratio with respect to the electrode unit.